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Radiative capture and photodisintegration reactions for the synthesis - - PowerPoint PPT Presentation

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Radiative capture and photodisintegration reactions for the synthesis of the p nuclei Philipp Scholz for the group of Prof. Dr. Andreas Zilges Institute for Nuclear Physics, University of Cologne Workshop on New Vistas in Low- Energy Precision

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Radiative capture and photodisintegration reactions

  • P. Scholz, AG Zilges, University of Cologne

Radiative capture and photodisintegration reactions for the synthesis of the p nuclei

Workshop on New Vistas in Low- Energy Precision Physics (LEPP)

April 4th-7th, 2016

Philipp Scholz

for the group of Prof. Dr. Andreas Zilges

Supported by the ULDETIS project within the UoC Excellence Initiative institutional strategy and by DFG (ZI 510/8-1,INST 216/544-1). * Partly supported by the Bonn-Cologne Graduate School of Physics and Astronomy.

Institute for Nuclear Physics, University of Cologne

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Outline Introduction

  • Nucleosynthesis of heavy elements and the p nuclei
  • the g-process reaction network

Experimental measurements of cross-sections

  • photo-inducedreaction measurements
  • charged-particleinduced reaction studies

Experimental results

  • testing the E1-strength in 90Zr via 89Y(p,g)
  • total and partial cross sections for 92Mo(p,g)
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

The synthesis of the p nuclei p nuclei

  • 30-35 neutron deficient isotopes
  • cannot be produced by neutron-

capture reactions

  • relativelylow isotopic abundances

in comparison to s- and r-isotopes

  • riginallythought to be produced

via proton-capture

  • temperatures would lead to

immediate photodisintegration

  • T. Rauscher et al., Rep. Prog. Phys. 76 (2013) 066201
  • M. Arnould et al., Phys. Rep. 450(2007) 97
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

The synthesis of the p nuclei g process reaction-network

  • huge photodisintegration reaction-network
  • at temperatures between 1.5 GK and 3 GK in

ccSN or type Ia SN

  • starting from stable seed nuclei formed in the

s- or r-process

  • g-process path proceeds first via (g,n) reactions
  • branching for A < 130 mainly via (g,p)
  • above A > 130 (g,a) get more important
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

reaction-network calculations

  • g-process network calculations cannot reproduce solar system abundance
  • ther contributions from rp-, a- or other processes?
  • problems with photoinduced reaction cross sections?

The synthesis of the p nuclei

S.E. Woosley and W. M. Howard, ApJSS 36 (1978) 285

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Experimental measurements of cross sections Photodisintegration

  • measuring cross sections via direct detectionof ejectilesor via photoactivation
  • using either monochromatic g-ray beams or Bremsstrahlung

b

separationenergy Sn or Sp

AX

g

n or p

A‘Y

g

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Experimental measurements of cross sections Ground-state contributions

  • measured cross sections cannot directly used for astrophysics
  • for g-induced reaction the ground-state contribution is almost zero
  • larger contribution from excited states in the stellar plasma (T9 > 1.5)
  • reaction rates are obtained from the inverse reactions via reciprocitytheorem

(g,n) (g,p) (g,a)

T . Rauscher, ApJSS 201 (2012) 26

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Experimental measurements of cross sections Statistical model

  • cross sections in the Gamow window

are small ( < µb)

  • most of the reactions are not

accessiblein the laboratory

  • reaction rates are calculated mostly in

the scope of the statistical model

  • cross-section measurements to

improve nuclear physics input- parameters:

  • g-strength function (also via (g,g’))
  • particle + nucleus optical model

potentials

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Charged-particle induced reaction cross sections

Activation technique

  • widely used technique for measureing cross-sections
  • temporal and spatial separation of irradiation and spectroscopy
  • no access to reactions involving stable reaction products
  • feasible half-lives neccessary
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SLIDE 10
  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Charged-particle induced reaction cross sections

Activation technique

  • widely used technique for measureing cross-sections
  • temporal and spatial separation of irradiation and spectroscopy
  • no access to reactions involving stable reaction products
  • feasible half-lives neccessary

4p summing crystal method

  • complete deexcitation is summed up in one peak
  • access to stable reaction products
  • need for very different Q-values for competing reactions
  • no access to partial cross-sections
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Charged-particle induced reaction cross sections

Activation technique

  • widely used technique for measureing cross-sections
  • temporal and spatial separation of irradiation and spectroscopy
  • no access to reactions involving stable reaction products
  • feasible half-lives neccessary

4p summing crystal method

  • complete deexcitation is summed up in one peak
  • access to stable reaction products
  • need for very different Q-values for competing reactions
  • no access to partial cross-sections

In-beam method with HPGe detectors

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam technique with HPGe detectors

  • de-excitation of the

entry state

  • determination of partial

cross sections

  • very sensitive on the g-ray

strength function

Ep + Q

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam technique with HPGe detectors

  • de-excitation of the

entry state

  • determination of partial

cross sections

  • very sensitive on the g-ray

strength function

  • transitions to the

ground state

  • determination of the total

cross section

Ep + Q

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SLIDE 14
  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam technique with HPGe detectors

  • 10 MV FN-Tandem ion

accelerator HORUS γ-ray spectrometer

  • 14 HPGe detectors
  • High resolution

≈ 2 keV @ 1332 keV

  • High total efficiency

≈ 2% @ 1332 keV

  • 5 different angles with respect

to beam axis

  • determination of angular

distributions

  • BGO shields
  • L. Netterdon et al., NIM A 754 (2014) 94-100
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam technique with HPGe detectors Target chamber

  • cooling trap
  • tantalum coating
  • independent current readouts
  • δ-electron suppression
  • built-in detector for Rutherford

Backscattering Spectrometry (RBS)

  • L. Netterdon et al., NIM A 754 (2014) 94-100
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

86Sr 87Sr 88Sr 89Y 90Zr 91Zr 92Zr 93Nb 94Mo 92Mo

  • reaction in a region which is normally

underproduced in reaction network calculations

  • total cross section was measured twice

before

  • g-ray strength function in 90Zr was

measured before

  • natural yttrium target (583µg/cm²)
  • beam currents between 1nA and 60nA
  • five different proton energies between

3.65 MeV and 4.70 MeV, i.e. g-ray energies between 7.71 MeV and 12.98 MeV (Q-Value: 8353.4 keV)

91Nb 93Tc 92Nb

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

  • L. Netterdon et al., PLB 744 (2015) 358

g0 g1 g2 g3 g4 g5

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

  • 89Y(p,g) partial cross sections: huge deviations
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

  • using g-strength function from (g,g’) measurement:
  • R. Schwengner et al., PRC 78 (2008) 064314
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

  • L. Netterdon et al., PLB 744 (2015) 358
  • adjusting g-strength to measured data
  • R. Schwengner et al., PRC 78 (2008) 064314
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 89Y(p,g)

  • L. Netterdon et al., PLB 744 (2015) 358
  • R. Schwengner et al., PRC 78 (2008) 064314

Impact on 90Zr(g,p)89Y

  • 15 % larger reaction rate than

based on E1-strength from (g,g‘)

  • twice as large as BRUSLIB reaction

rate (QRPA strength)

  • three times smaller than

NONSMOKER rates (Lorentzian- type E1-strength)

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam measurement of the 92Mo(p,g)

86Sr 87Sr 88Sr 89Y 90Zr 91Zr 92Zr 93Nb 94Mo 92Mo

  • 92Mo is the most abundant p nuclei and its
  • rigin is highly debated
  • total cross-sectionwere measured before with

different techniques at energies below 3.5 MeV

  • isotopicallyenriched 92Mo target (94 %)
  • beam currents between 50 nA and 350 nA
  • proton energies between 3.7 MeV and 5.4 MeV
  • extending measurement towards higher

energies

  • sensitive to higher energy g-ray

transitions

93Tc 91Nb 92Nb

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Problem: metastable state @ 391 keV

  • Significant half-life
  • Electron capture branching

to 93Mo Solution:

  • Determine σgs
  • Determine σm

In-beam measurement of the 92Mo(p,g)

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Total cross sections

  • Previously measured

cross sections show fluctuating behavior

  • TALYS calculations
  • Unsatisfactory

reproduction with default settings

  • modified γ-strengths
  • M1 shell model
  • Gogny-HFB + QRPA
  • Skyrme-HFB + QRPA
  • T. Sauter and F. Käppeler, PRC 55, 3127 (1997)
  • Gy. Gyürky et al., NPA 922, 112–125 (2014)
  • J. Mayer et al., PRC, accepted

In-beam measurement of the 92Mo(p,g)

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Total cross sections

  • T. Sauter and F. Käppeler, PRC 55, 3127 (1997)
  • Gy. Gyürky et al., NPA 922, 112–125 (2014)
  • J. Mayer et al., PRC, accepted

In-beam measurement of the 92Mo(p,g)

  • Previously measured

cross sections show fluctuating behavior

  • TALYS calculations
  • Unsatisfactory

reproduction with default settings

  • modified γ-strengths
  • M1 shell model
  • Gogny-HFB + QRPA
  • Skyrme-HFB + QRPA
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SLIDE 28
  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Total cross sections

  • T. Sauter and F. Käppeler, PRC 55, 3127 (1997)
  • Gy. Gyürky et al., NPA 922, 112–125 (2014)
  • J. Mayer et al., PRC, accepted

In-beam measurement of the 92Mo(p,g)

  • Previously measured

cross sections show fluctuating behavior

  • TALYS calculations
  • Unsatisfactory

reproduction with default settings

  • modified γ-strengths
  • M1 shell model
  • Gogny-HFB + QRPA
  • Skyrme-HFB + QRPA
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SLIDE 29
  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Total cross sections

  • T. Sauter and F. Käppeler, PRC 55, 3127 (1997)
  • Gy. Gyürky et al., NPA 922, 112–125 (2014)
  • J. Mayer et al., PRC, accepted

In-beam measurement of the 92Mo(p,g)

  • Previously measured

cross sections show fluctuating behavior

  • TALYS calculations
  • Unsatisfactory

reproduction with default settings

  • modified γ-strengths
  • M1 shell model
  • Gogny-HFB + QRPA
  • Skyrme-HFB + QRPA
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SLIDE 30
  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne
  • J. Mayer et al., PRC, accepted

In-beam measurement of the 92Mo(p,g) Partial cross sections

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Summary

  • the origin of the p nuclei is still unclear due to

astrophysical and nuclear physics uncertainties

  • direct measurements of (g,x) reaction rates can in

most cases not directly applied to reaction network calculations

  • reaction rates are usually calculated within the

statistical model and via reciprocity theorem from the inverse reactions

  • charged-particle induced reaction studies can be

used for the improvement of models for statistical properties of nuclei

  • g-ray strength functions
  • particle+nucleus optical model potentials
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Uncertainties for g process nucleosynthesis Astrophysical uncertainties

  • seed abundances from s- or r-process or

chemical evolution

  • temperature and density profiles
  • contribution from, for instance, a-process in

neutrino-driven wind scenarios or rp process in Type Ia X-ray bursts?

  • T. Rauscher et al., Rep. Prog. Phys. 76 (2013) 066201

S.E. Woosley and W. M. Howard, ApJSS36(1978) 285

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Uncertainties for g process nucleosynthesis Nuclear physics uncertainties

  • sensitivity study of the g process in ccSN
  • all p isotope abundances are sensitive to (g,n)

reaction rates

  • nly the lighter p nuclei are sensitive to (g,p)
  • (g,a) especially important for the production

factors of the heavier p isotopes

  • W. Rapp et al., ApJ 653 (2006) 474

(g,p) (g,n) (g,a)

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Experimental measurements of cross sections

Monochromatic g-ray beams

Example: HIgS @ Duke, TERAS @ Tsukuba

  • using Laser Compton-Backscattering to produce (quasi-) monochromatic g-rays
  • measuring (g,n) cross sections point-by-point until the neutron treshold
  • T. Kondo et al., Phys. Rev. C 86 (2012) 014316
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Experimental measurements of cross sections Bremstrahlung

  • simulating a planck distribution with many Bremsstrahlung spectra using different

endpoint energies

  • direct measurement of (g,n) reaction rate at a specific temperature
  • P. Mohr et al., PLB 488 (2000) 127
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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Experimental measurements of cross sections

4p-summing crystal

  • S. Quinn et al., Phys. Rev. C 89 (2014) 054611

SuN – NaI 4p summingdetector [NSCL]

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  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

Experimental measurements of cross sections

In-beam method with HPGe detectors

Nuclear astrophysics @ HORUS

  • L. Netterdon et al., NIM A 754 (2014) 94

89Y(p,g)

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SLIDE 39
  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam technique with HPGe detectors Target chamber

  • cooling trap
  • tantalum coating
  • independent current readouts
  • δ-electron suppression
  • built-in detector for Rutherford

Backscattering Spectrometry (RBS)

  • L. Netterdon et al., NIM A 754 (2014) 94-100
slide-40
SLIDE 40
  • P. Scholz, AG Zilges, IKP, Universität zu KölnRadiative capture and photodisintegration reactions
  • P. Scholz, AG Zilges, University of Cologne

In-beam technique with HPGe detectors Target chamber

Beam cooling trap current readout